The therapeutic effects of drugs against HIV are overcome by drug resistant HIV variants. We describe a yeast drug resistance 'trap' for discovery by rapid positive selection of drug resistant HIV protease variants. This 'trap' is an adaptation of the yeast interaction trap/two hybrid system (Brent and Ptashne, Cell 43: 729; Fields and Song, Nature 340:245). Transcription of specific reporter genes or selectable marker genes in yeast are to be put under the regulation of a element transcription activator protein. Genetic engineering will be used to construct a hybrid activator gene in which the two activator elements are joined by a segment of HIV pol polyprotein. The HIV portion of the hybrid will include the HIV protease and one or more of its cleavage substrate sites. Activation of transcription by this hybrid activator will be dependent upon the activity of the protease. Media are described which will allow growth of the drug resistance trap yeast cells only if the protease is active or only if the protease is inactive. Large libraries of mutant protease genes will be screened or selected from to discover HIV protease variants which are active despite the presence of protease inhibitory drugs. PROPOSED COMMERCIAL APPLICATION: This work will lead to the rapid detection of resistant mutations to AIDS drugs before they appear in the clinic. This will allow the proactive development of drug combinations that will specifically inhibit resistant forms of HIV.